PROJECT SUMMARY Rectal Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC) infections are common among men who have sex with men (MSM) attending sexually transmitted disease (STD) clinics and are associated with HIV acquisition and transmission. United States screening guidelines only recommend rectal GC/CT screening among MSM who report receptive anal intercourse (RAI). However, rectal sexual exposures such as rimming, fingering, and use of sex toys in the anus are common and are associated with rectal GC/CT among individuals who engage in RAI. What is not known, however, is the risk of rectal GC/CT among individuals who engage in some rectal sexual behaviors but do not engage in RAI. Further, animal models suggest that oral acquisition of CT may lead to rectal CT infection, though this has not been studied in humans. This has important clinical implications for cisgender women in particular, in whom autoinoculation from the rectum to the vagina could lead to substantial morbidity. The work we propose in this application will document the prevalence of rectal GC/CT among individuals who do not engage in RAI and will provide data to support or refute current rectal screening guidelines. We propose a cross-sectional study of 400 MSM and transgender women or non-binary/genderqueer individuals who have sex with men (together, TGWMSM) who have not had RAI ever or in the last 24 months. Prior to recruitment for the cross-sectional study, we will conduct 10-15 cognitive interviews with TGWMSM to develop and refine a sexual behavior questionnaire of non-RAI rectal sexual behaviors. For the cross-sectional study we will recruit individuals from three sites ? an urban STD clinic, an urban HIV/STI testing center, and a college campus. Participants will complete a detailed sexual behavior questionnaire and self-obtain a rectal specimen for GC and CT nucleic acid amplification testing (NAAT). Using these data we will examine the prevalence of rectal GC and CT by reported non-RAI rectal sexual exposure (e.g., rimming, use of sex toys) and will examine the independent association of each reported behavior and testing positive for rectal GC or CT. We will calculate the population attributable risk percent (PAR%) to determine the proportion of rectal GC or CT attributable to each sexual behavior. In the sub-population of individuals who report only receptive oral sex and no rectal exposures ? a proxy for cis- gender women ? we will separately estimate the risk of rectal CT to explore the hypothesis that oral sex may be a risk factor for rectal CT. The data generated from this study has the potential to change the Center for Disease Control and Prevention?s rectal GC/CT screening guidelines with potential subsequent reductions in community prevalence of infection. Moreover, the results of this study will inform the utility of a human challenge model to further elucidate the transmission of GC and CT between humans.